Thermostatically controlled piezo-crystal



Oct. 18, 1932. H, SCHUMACHER 1,882,989

THERMOSTATICALLY CONTROLLED PIEZO CRYSTAL Filedneo. 11, 1930 Patented Oct. 18, 1932 UNITED STATES PATENT CFFICE HANS SCHUMACHER, OF BERLIN-LICHTEREELDE-WEST, GERMANY, ASSIGNOR TO C. LORENZ AKTIENGESELLSCHAFT, OF BERLIN, GERMANY THERMOSTATICALLY CONTROLLED PIEZO-CRYSTAL Application led December 11, 1930, Serial No. 501,537, and in Germany December 18, 1929.

In order to broadcast and use constant.

Wave lengths, it is necessary in particular to have available such crystal arrangements as are adapted to ensure an extremelyl accurate maintenance of constancy in frequency. For the purpose of more clearly explaining the scope of this application, it may be stated that, in the matter of broadcasting with constant wave lengths, no such system is here described in which a central transmitting sta.- tion sends a constantfundamental frequency toscattered auxiliary transmitting stations; but this application is concerned with transmitt'ng apparatus which operates on a constant wave length and which is locally controlled. In order to maintain, in this instance, the same constancy of frequency as is required in broad-casting with equal Wave lengths Where a fundamental frequency is transmitted, quartz crystals must be used that are capable of producing exceedingly accurate results. In order to illustrate this,'an

y example Will be given, e. g., it is absolutely necessary, when transmitting with a 300 meter Wave, that the frequency be maintained exactly at about 20 Hertz. From these iigures alone, it follows that it is not possible to maintain the desired constancy of frequency with quartz crystals, as ordinarily used.

It has been suggested before, that a piece of quartz be immersed in a mixture of ice Water. By this means a very accurate maintenance of constancy in frequency can be obtained, but there are however certain diffculties sometimes in providing the necessary ice.

@ther proposals, such as apparatus to accommodate the quartz crystals in an artificially heated chamber, are not adapted to give the desired result, namely to obtain the required constancy of frequency.

A suitable form for one of the proposed means may be` obtained only by the present invention, in which a plurality of chambers are arranged one within the other, While the quartz crystal is placed within the innermost chamber.

An arrangement of this type is illustrated diagrammatically hy way of example in the drawing.

within an outer case 1, which may consist of sheet metal or Wood having a refractory lining, is provided a metal box 2, containing again another metal box 8. rl`he quartz crystal is mounted in box 4l. The temperatures to be maintained in the individual cases are controlled automatically by means of devices, Which are sensitive to changes of tem perature, preferably mercury thermometers` with fused-in contacts. The temperature of the atmosphere surrounding the piece of quartz Q mounted in the box 4 is gauged by means of the thermometer T1. The contact leads of the said thermometer are passed outside of the said arrangement by way of a blocking circuit S1. Outside of the total arrangement are provided some relays and sources of electric current (not shown) by means of which the heating coil H, in the space containing the piece of quartz is heated.

In these leads is again interposed a blocking circuit S2. The leads 5 and (i connected to the quartz crystals pass to the grid circuit of the tube R, the oscillations of which are kept constant by the said quartz crystal. The chamber 3 containingr both the chamber l Wit-h the piece of quartz and the tube. R with its oscillatory circuits, is n'iaintaiued at a constant temperature `with the aid of the thermometer T2. Theleads from the contacts of the thermometer are again passed .to the outside by Way of a blocking circuit S3', While the heating coil H2 is provided for the maintenance of the temperature constant. Tln` said heating coil however, is not arranged Within the chamber 3 in a ivay similar to that of the chamber containing the quartz crystal, hut outside of the chamber Q between the chamber l provided with heat insulation and the metal chamber Q. The. leads for supplying current to the tube are passed over the filter arrangement S1, which will prevent any flou' of high frequency current by way of the leads supplying the grid, heating devices and anodes. i

The adjustment of the thermometers is .such that b v means of the contact thermometer 'll an adjusted temperature is kept constant within a margin of :L -0.1 degreesl ccu'igi'adc. The. thermometer 'l2 of the box 3, containing both the case with the piece of quartz and the tube with its tuning means is maintained at a predetermined temperature to an accuracy of il degree centigrade.

Only by means of such an arrangement is it possible to obtain the requisite constancy, since with the presence of only one chamber, as has been customary up to the present, sudden changes of the temperature on the Outside of the chamber, which can never be "avoided, will cause a'deviation from the so that heating losses through the dielectric in the chamber is avoided as far as possible. The condenser C, being an adjustable condenser of high capacity, is provided With strong plates, good insulation and fine adjustment, so that in this way changes of the frequency are also avoided.

Use is made of the filter circuits Sl to vSi to permit the relays controlled by the thermometers being accommodated outside of the case. This is an additional advantage over present known circuits, in which the relay is directly mounted inside of the case.

It may of course appear to be simpler to mount the controlling relays directly Within the box, but it must be considered, that reare adjusted and they must lays of that class be accessible to continuous control. If these controlling relays be arranged Within the box however, control thereof is'only possible by opening the whole arrangement as represented. If these relays however are arranged outside, adjustment can be Iliade at Once in a simple manner, without the necessity of dismantling the Whole apparatus. In order to do. this, however, it` is necessary to cut in the filter circuits, as described. Furthermore it is naturally of advantage to screen oif all leads against the action of high frequency currents in well known Ways, in order to prevent the entrance of any high frequency oscillations.

The next circuit coupled to the coil L may be of such dimension that the resulting grid control potential is only a small portion of that necessary to keep the tube of the next amplifying step Within the negative range of its characteristic curve. By this means reactions due to changes of load are avoided in an effective manner. By means of this arrangement constancy of the frequency can be obtained, Which is equivalent to that of broadcasting on equal Wave lengths when using a fundamental transmitted frequency, as used at the present time.

I claim:

l. In a temperature control system, the combination of a plurality of chambers one Within the other, a source of oscillations, a piezo-electric crystal disposed in the innermost chamber for controlling said source of oscillations, said oscillator' and its associated circuits being disposed in the next outer chamber, and means in each of said chambers for approximately maintaining a predetermined temperature therein, the actual temperature in each of said chambers differing from said predetermined temperature by a smaller amount until the innermost chamber is reached at Which point the temperature becomes substantially constant.

2. In a temperature control system, the combination of a plurality of chambers one Within the other, a source of oscillations, means disposed in the innermost chamber for controlling said source of oscillations, said oscillator and its associated circuits being disposed inthe next outer chamber, and thermostats in each of said chambers for approximately maintaining a predetermined temperature therein, the actual temperature in each of said chambers being such that the temperature of the outermost chamber differs most from the predetermined temperature, the temperature of the succeeding inner chambers differing progressively less from the predetermined temperature, the temperature of the innermost chamber remaining substantially equal to said predetermined temperature.

3. In a temperature control system, the combination of a plurality of chambers one within the other, an oscillating vacuum tube, a piezo-electric crystal disposed in the innermost chamber for controlling the oscillations of said tube, said tube and its associated circuits being disposed in the next outer chamber, thermostatically controlled means in each of said chambers for approximately maintaining a predetermined temperature therein, the actual temperature in each of said chambers differing from said predetermined temperature by a progressively smaller amount until the innermost chamber is reached, the temperature therein being maintained substantially constant.

In testimony whereof I affix my signature.

HANS SCHUMACHER. 

